FIG. 6 is a side sectional view of a conventional washing machine. The washing machine has an outer casing 101, a top cover 105 covering the upper side of the outer casing 101, an outer tub 111 suspended by a suspension in the outer casing 101, a washing tub 113 rotatably installed in the outer tub 111, a pulsator 115 installed on the bottom of the washing tub 113, and a driving motor 118 for driving the pulsator 115.
During the washing operation, the driving motor 118 rotates the pulsator 115, and by the water-flow vortex generated in such a situation, the laundry in the washing tub 113 is washed. During the dehydrating operation, the pulsator 115 and the washing tub 113 are rotated together at a high speed, and the laundry is dehydrated by the centrifugal force generated in that situation.
During the washing operation, the water in the washing tub 113 contains dirt detached from the laundry, and if the washing water contains too much dirt, the washing effect is lowered. Thus, the washing machine is equipped with a device for filtering dirt in the washing water.
The filtering device is comprised of a circulation duct 125 formed vertically on the inner wall of the washing tub 113, and a filtering web 127 installed on the upper end of the circulation duct 125. The lower end of the circulation duct 125 is open at the lower area of the washing tub 113, and the upper end thereof is open at the upper area of the washing tub 113.
By the centrifugal force of the water-flow vortex generated in the washing tub 113, the washing water in the washing tub 113 flows into the circulation duct 125 through the lower opening of the circulation duct 125. The water in the circulation duct 125 is moved up along the circulation duct 125, and then is supplied again into the washing tub 113. In this situation, the dirt contained in the re-supplied washing water is filtered by the filtering web 127, and accordingly, the washing water in which dirt has been filtered is supplied into the washing tub 113.
However, in such a conventional washing machine, the filtering efficiency is lowered gradually as the dirt is accumulated in the filtering web 127, so the filtering web 127 must be cleaned frequently. And, the filtering web 127 is apt to wear, so it should be exchanged with a new one frequently. Furthermore, there is another shortcoming that the small and weighty dirt such as sand cannot be filtered well.